The present invention relates to a method for depositing a conductive layer on an insulating layer, and relates more particularly to a method for depositing a conductive layer on an insulating layer for a built-up circuit board.
A so-called built-up circuit board is conventionally known as a high-density circuit board wherein an insulating layer and a conductive circuit layer are alternately laminated on a base substrate, on the surface of which a conductive circuit is plated. In the process for manufacturing the built-up circuit board, generally, a conductive (metal) layer is formed on the insulating layer of the base substrate by plating.
When the insulating layer is composed of a resin, generally, a pre-process for roughing the surface of the resin layer before metal plating is performed in order to increase the strength of the adhesion between the resin and the plated metal. Oxidization of the surface of the resin layer is one approach and may be performed using an oxidizing agent such as permanganate or chromic acid. During this process, the oxidization effect etches the surface of the resin layer and tiny raised and recessed portions are formed in it (that is, the surface is roughened). Before this oxidization process is employed, however, a process called surface swelling is performed. During the swelling process, the surface of the resin layer is softened (steeped) by applying to it a processing liquid containing an aqueous organic solvent and a strong alkali, such as calcined soda. Since the surface is softened, greater adhesion is possible by the subsequent oxidization (etching) process.
However, the conventional swelling process is plagued with the following problems:
(a) Since stable performance of the swelling process is not easily predictable, the surface of the resin layer often is not uniformly (evenly) softened. As a result, during the oxidization process the surface of the resin layer is not uniformly oxidized and etched, and the strength of the adhesion acquired by the metal plated layer, which is formed later, is reduced in some areas. To reduce this unstable swelling, frequently the effects (the state of the softened surface) of the swelling process must be examined, and/or the composition of the processing liquid adjusted.
(b) Since the processing liquid that is used contains an aqueous organic solvent and a strong alkali, such as calcined soda, it is normally applied at a temperature of 40 to 100C., to prevent the generation of a solvent steam that can adversely affect the environment.
A primary object of the present invention is the resolution of the above conventional problems.
It is another, more specific object of the present invention to provide an innovative resin softening process to replace the conventional swelling process that more stably and uniformly softens the surface of a resin insulating layer.
It is yet another object of the present invention to provide a more reliable built-up circuit board by increasing the adhesive strength of the bond between a metal plated layer and a resin insulating layer, by more stably and more uniformly softening the surface of the insulating layer.
It is still an additional object of the present invention to prevent the swelling process liquid from adversely affecting the environment, by reducing the amount of the fluid that is required.
According to one embodiment of the present invention, there is provided a method for depositing a conductive layer on an insulating layer comprising the steps of preparing a substrate having an insulating layer, irradiating selected portions of the insulating layer with ultraviolet light, oxidizing the selected portions of the insulating layer that have been irradiated with the ultraviolet light, and depositing the conductive layer on the selected portions of the insulating layer that have been oxidized.
Furthermore, according to another embodiment of the present invention, a method is provided for manufacturing a built-up circuit board and including the steps of preparing a substrate, on the surface of which a conductive circuit is plated, depositing a patterned resin layer on the substrate, irradiating selected portions of the surface of the resin layer with ultraviolet light, performing an oxidizing process on selected portions of the surface of the resin layer that has been irradiated with the ultraviolet light, plating a conductive layer on the resin layer for which the oxidizing process has been performed, and patterning the conductive layer to form an electrical circuit.